The oxidative condensation reaction of methane is conventionally termed the oxidative coupling of methane. This method allows production of ethane, ethylene and usually small amounts of higher hydrocarbons (hereinafter referred to as C.sub.2+) from methane. Deleteriously, however, the total oxidation of methane to water and oxides of carbon usually accompanies the oxidative coupling reaction.
Typically, a tubular fixed bed reactor is utilized in which to carry out the reaction Two different procedures for feeding the reactant gases into the reactor have been used in prior art processes. In the first case, oxygen and methane were introduced at the entrance of the tubular reactor in a cycling mode. Thus, oxygen only was fed to the reactor for a given period, followed by inert gas and subsequently, methane only was fed to the reactor for a given period. In the second case, oxygen and methane were introduced at the entrance of the tubular reactor simultaneously. Thus CH.sub.4 and O.sub.2 were co-fed to the reactor unit.
The oxidative coupling of methane has been extensively studied during recent years. In particular, the development of catalysts functional to enhance C.sub.2+ yield has been of interest More specifically, catalysts have been prepared which have included most elements of the periodic table and/or their oxides, and/or their salts thereof, either singly or in admixture. It has been determined with all the known catalysts investigated that an apparent limit to the yield of C.sub.2+ of about 25% exists mainly because of the role of the gas phase reactions.
Higher C.sub.2+ yields in oxidative coupling of methane are obtainable by increasing the methane conversion or the C.sub.2+ selectivity or both. Unfortunately, higher selectivity is usually observed at lower conversion for this process The selectivity is the most important factor in the practical application of the coupling reaction. If the selectivity is high a high C.sub.2+ yield may be achieved by recycling the reactants.
Exemplary prior art processes are described in U.S. Pat. Nos. 4,523,049, 4,523,044, 4,665 259, 4,560,821, 4,523,050 or 4,499,323. It would be advantageous if a process could be found which would overcome the limitative yield which occurs with these prior art processes.